One of the concerns raised about the American system is that the proposed identity documents, which transmit data to special receivers, may betray the presence of US citizens to terrorists who could use that functionality to identify targets:
Some privacy groups oppose the introduction of e-passports because the
chips wirelessly transmit personal information to special receivers via
radio signal. They fear anyone with the right equipment could scan a
crowd for Americans, making them targets for attack or surveillance.
The privacy concerns have not deterred the government from pursuing its
e-passport project, one of the many efforts it launched to bolster
national security after the Sept. 11, 2001 terrorist attacks. The State
Department said last year that it plans to produce more than 1 million e-passports this year and issue them initially to citizens through the Los Angeles Passport Agency.
I am pretty excited about these trends and I am interested to see how the security concerns are addressed.
(via CNET News.com)